Performance Tuning

Overview

This guide covers performance optimization across video encoding, audio processing, capture pipeline, and network configuration. All settings reference actual configuration from config.json.

Video Encoding Optimization

Bitrate Configuration

Balance quality and latency with bitrate settings:

{
  "video": {
    "bitrateStart": 8000000,  // 8 Mbps - initial bitrate
    "bitrateMin": 8000000,    // 8 Mbps - minimum allowed
    "bitrateMax": 12000000    // 12 Mbps - maximum allowed
  }
}

Tuning Guidelines:

Resolution	Min Bitrate	Recommended	Max Bitrate	Notes
1080p@60fps	6 Mbps	8-10 Mbps	12 Mbps	Default config
1080p@120fps	10 Mbps	12-15 Mbps	20 Mbps	High motion
1440p@60fps	10 Mbps	12-16 Mbps	20 Mbps	Higher resolution
4K@60fps	20 Mbps	25-35 Mbps	50 Mbps	Requires tier expansion

Network Conditions:

Excellent (< 20ms, < 1% loss): Use bitrateMax
Good (20-50ms, 1-2% loss): Use bitrateStart
Fair (50-100ms, 2-5% loss): Reduce to bitrateMin
Poor (>100ms, >5% loss): Consider reducing bitrateMin

Encoder Presets

NVENC preset affects encoding speed and quality:

{
  "video": {
    "preset": "p2",  // p1 (fastest) to p7 (slowest)
    "rc": "cbr"      // Rate control: cbr, vbr, or vbr_hq
  }
}

Preset Selection:

p1 - Fastest, lowest quality, ~1-2ms encoding latency
p2 - Fast, good quality, ~2-3ms latency (default)
p3 - Balanced, better quality, ~3-5ms latency
p4 - High quality, ~5-8ms latency
p5-p7 - Highest quality, 10-20ms+ latency (not recommended for streaming)

Rate Control Modes:

cbr (Constant Bitrate) - Predictable bandwidth, best for streaming
vbr (Variable Bitrate) - Better quality, less predictable
vbr_hq - Highest quality, highest latency

Advanced Encoder Settings

{
  "video": {
    "bf": 0,              // B-frames: 0 for lowest latency
    "rcLookahead": 0,     // Rate control lookahead: 0 for real-time
    "asyncDepth": 2,      // Async encoding depth
    "surfaces": 3,        // Surface count for pipeline
    "ignorePli": false,   // Respond to Picture Loss Indication
    "minPliIntervalMs": 3000,        // Min 3s between keyframes
    "minPliLossThreshold": 0.15,     // 15% loss before forcing keyframe
    "fullRange": false    // Use limited color range
  }
}

Low-Latency Profile:

{
  "preset": "p1",
  "rc": "cbr",
  "bf": 0,
  "rcLookahead": 0,
  "asyncDepth": 1,
  "surfaces": 2
}

High-Quality Profile:

{
  "preset": "p3",
  "rc": "vbr_hq",
  "bf": 2,
  "rcLookahead": 8,
  "asyncDepth": 3,
  "surfaces": 4
}

Bitrate Adaptation

Automatic bitrate adjustment based on network conditions:

{
  "video": {
    "bitrateController": {
      "increaseStepBps": 1000000,    // Increase by 1 Mbps
      "decreaseCooldownMs": 1000,     // Wait 1s after decrease
      "cleanSamplesRequired": 3,      // 3 good samples before increase
      "increaseIntervalMs": 1000      // Check every 1s
    }
  }
}

Tuning for Stability:

Increase cleanSamplesRequired to 5-10 for more stable bitrate
Increase decreaseCooldownMs to 2000-3000ms to prevent oscillation
Reduce increaseStepBps to 500000 (500 Kbps) for gradual ramp-up

Frame Rate Pacing

{
  "video": {
    "fps": 60,
    "pacingFixedUs": 16666  // 16.666ms = 60fps
  }
}

Common Frame Rates:

30fps: pacingFixedUs: 33333
60fps: pacingFixedUs: 16666 (default)
90fps: pacingFixedUs: 11111
120fps: pacingFixedUs: 8333
144fps: pacingFixedUs: 6944

Audio Latency Optimization

Frame Size and Buffering

Smaller frame sizes reduce latency but increase CPU overhead:

{
  "audio": {
    "frameSizeMs": 10,     // 10ms frames (lowest latency)
    "bitrate": 80000,      // 80 kbps Opus
    "complexity": 6,       // Opus complexity 0-10
    "enableFec": true,     // Forward Error Correction
    "enableDtx": false,    // Discontinuous Transmission
    "application": 2049    // OPUS_APPLICATION_RESTRICTED_LOWDELAY
  }
}

Frame Size Trade-offs:

Frame Size	Latency	CPU Usage	Packet Rate
5ms	~5ms	Very High	200 pkt/s
10ms	~10ms	High	100 pkt/s (default)
20ms	~20ms	Medium	50 pkt/s
40ms	~40ms	Low	25 pkt/s

Recommendation: Use 10ms for competitive gaming, 20ms for casual use.

Ultra-Low Latency Mode

{
  "audio": {
    "latency": {
      "enforceSingleFrameBuffering": true,   // No buffering
      "maxFrameSizeMs": 10,
      "minFrameSizeMs": 10,
      "strictLatencyMode": false,            // Set true for absolute minimum
      "warnOnBuffering": true,
      "targetOneWayLatencyMs": 40,           // Glass-to-glass target
      "ultraLowLatencyProfile": false,       // Experimental <30ms mode
      "disableFecInLowLatency": false        // Keep FEC enabled
    }
  }
}

Ultra-Low Profile (Experimental):

{
  "frameSizeMs": 5,
  "strictLatencyMode": true,
  "ultraLowLatencyProfile": true,
  "targetOneWayLatencyMs": 25
}

⚠️ Warning: Ultra-low latency increases CPU usage and packet loss sensitivity.

Audio Bitrate Adaptation

{
  "audio": {
    "bitrateAdaptation": {
      "enabled": true,
      "minBitrate": 64000,            // 64 kbps minimum
      "maxBitrate": 128000,           // 128 kbps maximum
      "decreaseCooldownMs": 2000,     // 2s cooldown after decrease
      "increaseIntervalMs": 10000,    // Check every 10s
      "increaseStep": 8000,           // Increase by 8 kbps
      "highLossThreshold": 0.05,      // 5% loss triggers decrease
      "lowLossThreshold": 0.01,       // <1% loss allows increase
      "cleanSamplesRequired": 30,     // 30 good samples for increase
      "fecEnableThreshold": 0.03,     // Enable FEC at 3% loss
      "fecDisableThreshold": 0.005    // Disable FEC below 0.5% loss
    }
  }
}

Conservative Profile:

{
  "decreaseCooldownMs": 5000,
  "increaseIntervalMs": 20000,
  "cleanSamplesRequired": 60
}

WASAPI Configuration

{
  "audio": {
    "wasapi": {
      "preferExclusiveMode": false,       // Exclusive mode for lowest latency
      "enforceEventDriven": true,         // Event-driven capture
      "devicePeriodMs": 5.0,              // 5ms period
      "fallbackPeriodMs": 10.0,           // Fallback to 10ms
      "force48kHzStereo": true,           // Always use 48kHz stereo
      "preferLinearResampling": true,     // Fast resampling
      "useDmoOnlyForHighQuality": false   // Use fast DMO
    }
  }
}

Exclusive Mode Trade-off:

✅ Pros: 2-3ms lower latency, more consistent timing
❌ Cons: Blocks other applications from audio device

Capture Performance

MMCSS Priority

Multimedia Class Scheduler Service ensures consistent timing:

{
  "capture": {
    "mmcss": {
      "enable": true,
      "priority": 4  // 1 (low) to 7 (critical)
    }
  }
}

Priority Levels:

1-2: Background capture
3-4: Normal streaming (recommended)
5-6: High priority for demanding games
7: Critical priority (may starve other processes)

Go Thread Priority:

// gortc_main/main.go:52-63
static void SetupGoThreadMMCSS(void) {
    DWORD taskIndex = 0;
    goMMCSSHandle = AvSetMmThreadCharacteristicsA("Pro Audio", &taskIndex);
    if (goMMCSSHandle != NULL) {
        SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_HIGHEST);
    }
}

Frame Pool and Queue Depth

{
  "capture": {
    "copyPoolSize": 4,           // GPU copy operation pool
    "maxQueueDepth": 2,          // Max frames in encode queue
    "framePoolBuffers": 2,       // Frame buffer pool size
    "minUpdateInterval100ns": 166666  // Min 16.666ms between frames (60fps)
  }
}

Low-Latency Profile:

{
  "copyPoolSize": 2,
  "maxQueueDepth": 1,
  "framePoolBuffers": 2
}

High-Throughput Profile:

{
  "copyPoolSize": 6,
  "maxQueueDepth": 3,
  "framePoolBuffers": 3
}

Skip Unchanged Frames

{
  "capture": {
    "skipUnchanged": true,         // Skip duplicate frames
    "dropWindowMs": 500,           // Window for drop detection
    "dropMinEvents": 12            // Min events before dropping
  }
}

Reduces bandwidth and CPU for static content (menus, lobbies).

Adaptive Backoff

{
  "capture": {
    "adaptiveBackoff": false,         // Enable adaptive frame skipping
    "adaptiveWindowMs": 2000,         // 2s monitoring window
    "adaptiveEagainThreshold": 8      // EAGAIN threshold
  }
}

Set adaptiveBackoff: true if capture frequently reports DXGI_ERROR_WAIT_TIMEOUT.

Network Optimization

TURN Server Placement

For clients behind restrictive NAT/firewalls: Environment Variables:

# Single TURN server
PION_TURN_URL="turn:turn.example.com:3478"
PION_TURN_USERNAME="username"
PION_TURN_CREDENTIAL="password"

# Multiple TURN servers (comma-separated)
PION_TURN_URLS="turn:us-west.example.com:3478,turn:us-east.example.com:3478"

Metered TURN Configuration:

// mm_server/Matchmaker.js:16-52
const { domain, apiKey, expirySeconds } = config.metered;
const iceServers = await getIceServers();
// Returns: [{ urls: 'stun:...' }, { urls: 'turn:...', username: '...', credential: '...' }]

Placement Best Practices:

Deploy TURN servers in same region as hosts
Use multiple TURN servers for redundancy
Monitor TURN bandwidth usage (relay is expensive)
Set expirySeconds to match average session length (default: 3600s)

ICE Configuration

WebRTC connection establishment:

// Default ICE configuration
const iceServers = [
  { urls: 'stun:stun.l.google.com:19302' },  // Google STUN
  { 
    urls: ['turn:turn.example.com:3478'],
    username: 'user',
    credential: 'pass'
  }
];

Connection Priority:

Host - Direct connection (lowest latency)
Server Reflexive - Via STUN (low latency)
Relay - Via TURN (higher latency, always works)

Buffer Pool Optimization

// gortc_main/main.go:780-784
var sampleBufPool = &tieredBufferPool{
    sizes: [13]int{128, 256, 512, 1500, 4096, 8192, 
                   16384, 32768, 65536, 131072, 262144, 524288, 1048576},
    sizeCount: 13,
}

Tiers Explained:

128-512B: Audio frames, small RTP packets
1500B: Standard MTU size
4KB-32KB: 1080p video frames
64KB-256KB: 4K low-motion frames
512KB-1MB: 4K high-motion frames

Memory Tuning:

// init (gortc_main/main.go:787-818)
preallocCounts := [13]int{6, 6, 5, 4, 3, 2, 2, 1, 1, 1, 0, 0, 0}

Reduce preallocation counts if memory is constrained.

Input Processing Optimization

Adaptive Quality Control

{
  "input": {
    "adaptiveQualityControl": {
      "enableAdaptiveDropping": true,
      "rttExcellentThreshold": 10.0,
      "rttGoodThreshold": 50.0,
      "rttFairThreshold": 100.0,
      "rttPoorThreshold": 200.0,
      "statsUpdateIntervalMs": 100
    }
  }
}

Input events are prioritized based on network conditions.

Thread Priority

{
  "input": {
    "threadPriority": {
      "enableMMCSS": true,
      "mmcssClass": "Games",
      "enableTimeCritical": true,
      "threadPriority": 15,
      "taskName": "InputInjection"
    }
  }
}

Priority 15 = THREAD_PRIORITY_TIME_CRITICAL for lowest input latency.

Garbage Collection Tuning

// gortc_main/main.go:1291-1301
func init() {
    // GOGC=150 means GC runs when heap is 1.5x live set
    // Lower = more frequent GC, less memory
    // Higher = less frequent GC, more memory
    debug.SetGCPercent(150)
}

Memory Constrained:

debug.SetGCPercent(100)  // GC at 2x live heap

Performance Critical:

debug.SetGCPercent(200)  // GC at 3x live heap (original setting)

Performance Monitoring

Track these metrics to validate tuning: Video:

Glass-to-glass latency < 50ms
Encoder latency < 5ms
Frame drops < 1%
Bitrate stability (±10% variance)

Audio:

One-way latency < 40ms
Packet loss < 2%
No buffer underruns
Queue depth < 2.0 average

Capture:

Frame time consistency (low jitter)
GPU copy time < 1ms
Queue never reaches maxQueueDepth

Network:

RTT < 50ms
Jitter < 5ms
ICE connection via host/srflx (not relay)

Next Steps

Monitoring - Track performance metrics
Troubleshooting - Fix performance issues

Getting Started

Deployment

Components

Configuration

Operations

Overview

Video Encoding Optimization

Bitrate Configuration

Encoder Presets

Advanced Encoder Settings

Bitrate Adaptation

Frame Rate Pacing

Audio Latency Optimization

Frame Size and Buffering

Ultra-Low Latency Mode

Audio Bitrate Adaptation

WASAPI Configuration

Capture Performance

MMCSS Priority

Frame Pool and Queue Depth

Skip Unchanged Frames

Adaptive Backoff

Network Optimization

TURN Server Placement

ICE Configuration

Buffer Pool Optimization

Input Processing Optimization

Adaptive Quality Control

Thread Priority

Garbage Collection Tuning

Performance Monitoring

Next Steps

​Overview

​Video Encoding Optimization

​Bitrate Configuration

​Encoder Presets

​Advanced Encoder Settings

​Bitrate Adaptation

​Frame Rate Pacing

​Audio Latency Optimization

​Frame Size and Buffering

​Ultra-Low Latency Mode

​Audio Bitrate Adaptation

​WASAPI Configuration

​Capture Performance

​MMCSS Priority

​Frame Pool and Queue Depth

​Skip Unchanged Frames

​Adaptive Backoff

​Network Optimization

​TURN Server Placement

​ICE Configuration

​Buffer Pool Optimization

​Input Processing Optimization

​Adaptive Quality Control

​Thread Priority

​Garbage Collection Tuning

​Performance Monitoring

​Next Steps

Overview

Video Encoding Optimization

Bitrate Configuration

Encoder Presets

Advanced Encoder Settings

Bitrate Adaptation

Frame Rate Pacing

Audio Latency Optimization

Frame Size and Buffering

Ultra-Low Latency Mode

Audio Bitrate Adaptation

WASAPI Configuration

Capture Performance

MMCSS Priority

Frame Pool and Queue Depth

Skip Unchanged Frames

Adaptive Backoff

Network Optimization

TURN Server Placement

ICE Configuration

Buffer Pool Optimization

Input Processing Optimization

Adaptive Quality Control

Thread Priority

Garbage Collection Tuning

Performance Monitoring

Next Steps